In general, Cu—Fe—P copper alloys have been previously used as copper alloys for semiconductor IC lead frames. Examples of these Cu—Fe—P copper alloys include a copper alloy (C19210 alloy) containing 0.05% to 0.15% of Fe and 0.025% to 0.040% of P and a copper alloy (CDA194 alloy) containing 2.1% to 2.6% of Fe, 0.015% to 0.15% of P, and 0.05% to 0.20% of Zn. Among copper alloys, these Cu—Fe—P copper alloys exhibit high strength, high electrical conductivity, and high thermal conductivity when an intermetallic compound, e.g., Fe or Fe and P, is dispersed in a copper matrix, and therefore, these have been generally used as the international standard alloys.
In recent years, as a semiconductor device has been required to have a larger capacity, a smaller size, and higher integration, the cross-sectional area of an IC lead frame is being reduced, and higher levels of strength, electrical conductivity, and thermal conductivity are required. With the trends, a copper alloy component used for an IC lead frame in a semiconductor device is required to have yet higher strength, electrical conductivity, and thermal conductivity.
For example, guidelines of the above-described increase in strength and increase in electrical conductivity required of the copper alloy sheet used for the IC lead frame are the strength of the copper alloy sheet of 150 Hv or more in terms of hardness and the electrical conductivity of 75% IACS or more. The situation of the increase in strength and the increase in electrical conductivity is also applicable to a copper alloy used for not only IC lead frames but also other electrically conductive components such as connectors, terminals, switches, relays, etc., in electric and electronic components.
An advantage of the above-described Cu—Fe—P copper alloy is that it has a high electrical conductivity and, in order to increase its strength, a means of increasing the contents of Fe and P or adding Sn, Mg, Ca, or the like as a third element has so far been taken. However, the increase of the amount of such elements causes strength to be increased but an electrical conductivity to deteriorate inevitably. Therefore, it has been difficult merely by controlling the chemical composition of a copper alloy to realize a Cu—Fe—P copper alloy having a good balance between a higher electrical conductivity and a higher strength or simultaneously having both the properties which are required along with the above-described trends of a larger capacity, a smaller size, and higher integration of a semiconductor device.
To cope with the difficulty, it has hitherto been proposed to control the microstructure or the precipitation state of dispersoids in a Cu—Fe—P copper alloy. For example, a copper alloy having a high strength and high electrical conductivity is proposed in which chemical compounds containing Fe and P of 0.2 μm or less are homogeneously dispersed (refer to Patent Document 1).
The copper alloy sheet used for IC lead frames, terminals, connectors, switches, relays, and the like is required to have excellent bendability capable of enduring sharp bending, e.g., U-bending or 90° bending after notching, as well as the high strength and the high electrical conductivity.
However, the above-described addition of solid-solution hardening elements, e.g., Sn and Mg, or the increase in strength by increasing reduction ratios of the cold rolling inevitably cause deterioration of the bendability and, therefore, the required strength and the bendability cannot become mutually compatible.
On the other hand, it is known that the bendability can be improved to some extent by grain refining or by controlling the state of dispersoids (refer to Patent Documents 2 and 3). However, in order to produce a Cu—Fe—P high-strength materials (the hardness of copper alloy sheet is 150 Hv or more, and the electrical conductivity is 75% IACS or more) compatible with reduction in the size and weight of electronic components in recent years, an increase in the quantity of work hardening by increasing reduction ratio of the cold rolling becomes indispensable.
Consequently, as for the above-described high-strength materials, the bendability cannot be adequately improved against the above-described sharp bending e.g., U-bending or 90° bending after notching, by means of microstructure control, e.g. grain refining or control of the state of dispersoids, disclosed in Patent Documents 1, 2, and 3.
On the other hands as for Cu—Fe—P copper alloys, it is proposed to control the microstructure (refer to Patent Documents 4 and 5). Specifically, it is proposed in Patent Document 4 that an intensity ratio, I(200)/I(220), of X-ray diffraction of (200) to X-ray diffraction of (220) of the copper alloy sheet is 0.5 or more and 10 or less, the density of Cube orientation: D(Cube orientation) is 1 or more and 50 or less, or a ratio, D(Cube orientation)/D(S orientation) of the density of Cube orientation: D(Cube orientation) to the density of S orientation: D(S orientation) is 0.1 or more and 5 or less.
It is proposed in Patent Document 5 that an intensity ratio, [I(200)+I(311)]/I(220), of the sum of X-ray diffraction of (200) and X-ray diffraction of (311) to X-ray diffraction of (220) is 0.4 or more.    [Patent Document 1] Japanese Unexamined Patent Application Publication No. 2000-178670 (Claims)    [Patent Document 2] Japanese Unexamined Patent Application Publication No. 6-235035 (Claims)    [Patent Document 3] Japanese Unexamined Patent Application Publication No. 2001-279347 (Claims)    [Patent Document 4] Japanese Unexamined Patent Application Publication No. 2002-339028 (Claims, paragraphs 0020 to 0030)    [Patent Document 5] Japanese Unexamined Patent Application Publication No. 2000-328157 (Claims, examples)